Co2Fe(Ti0.5Al0.5) epitaxial thin films: Structural and magnetic properties of a Heusler alloy with Z-site transition metal substitution

We investigate the structural, static, and dynamic magnetic properties of epitaxial Heusler Co ₂Fe(Ti _0.5 Al _0.5 ) (CFTA) alloy thin films with thickness varying from 6 nm to 80 nm grown by sputter beam epitaxy on cubic MgO(001), MgAl 2 O 4 (001), and hexagonal Al 2 O 3 (11 2 ̄ 0) substrates. X-ray diffraction measurements indicate epitaxial growth of CFTA thin films with B2 chemical ordering, with cubic [001] and [220] CFTA axes normal to the cubic and hexagonal substrates, respectively. Microstructure analysis of films grown on MgO substrates reveals a uniformly oriented epitaxial crystal with small variations consistent with strain distortions, providing an explanation for the relatively large X-ray rocking curve values found. Meanwhile, films on Al 2 O 3 (11 2 ̄ 0) substrates reveal columnar growth with frequent in-plane grain rotations. A pronounced four-fold magnetocrystalline anisotropy is observed in epitaxial thin films grown on cubic substrates. A pronounced uniaxial anisotropy for films grown on Al 2 O 3 (11 2 ̄ 0) substrates is observed. A saturation magnetization of ∼ 5 . 0 μ B /f.u. (where f.u. represents formula unit) is obtained at room temperature, slightly smaller compared to the expected value based on the Slater-Pauling rule. Ferromagnetic resonance spectroscopy finds an effective damping parameter and inhomogeneous linewidth broadening comparable to those found in parent compound Co ₂ FeAl, which suggests that Ti substitution can be achieved without negatively affecting the magnetic properties of the system.